Putrescine:pyruvate aminotransferase, a pyridoxal phosphate dependent enzyme with good stability and high catalytic efficiency, has been discovered and partially purified from Mycobacterium phlei. Since this enzyme represents an unexplored class of putrescine metabolizing enzymes, it will be further purified to homogeneity and some of its physical properties determined. To assess the significance of this class of aminotransferase in the regulation of intracellular putrescine levels, irreversible inactivators based on the concept of suicide substrates will be developed for this enzyme. Classes of compounds proposed as such mechanism-based inactivators include beta, gamma unsaturated diamines which should be substrates for the enzyme, allenic diamines, and beta, gamma unsaturated amino acids so that inactivation of the enzyme in the forward and reverse directions can be compared. Certain diamines containing a cyclopropylamine function are also suggested as a new type of inactivator for this class of diamine: alpha-keto acid aminotransferase. It is further suggested that mechanism based inactivators can be incorporated into multisubstrate adduct reversible inhibitors to produce highly selective and powerful irreversible inactivators. An analog of B6 capable of reacting specifically with arginine residues in the binding site for the phosphate group of the coenzyme is proposed for use with this amino-transferase and with B6 dependent enzymes in general.